Clamping assemblies of the above-mentioned type are used particularly, but not exclusively, in linear hydraulic winches. In this context, reference may be made, for example, to U.S. Pat. No. 4 615 509 or to the corresponding European patent No. 0 220 968, or indeed to the following U.S. Pat. Nos.: 2 400 514, 3 758 922, 3 762 512, and 4 381 584. A first spring is usually associated with each set of rollers and acts on the mounting frame of said rollers in order to preposition or preset the rollers in a position such that when the associated jaw moves from its second position towards its first position, i.e. towards the clamping position, then the set of rollers is capable of accompanying the jaw as it moves, by rolling over one of two opposite surfaces of the passages through the body of the clamping assembly and over the facing surface of the jaw (see U.S. Pat. Nos. 2 400 514 and 3 762 512). In addition, each jaw is sometimes also associated with a respective second spring different from the first spring, said second spring usually being interposed between the associated jaw and the body of the clamping assembly in such a manner as to urge the jaw towards its first or clamping position.
In addition, it is sometimes also necessary to be able to control the jaws positively, e.g. in order to hold them in the second or un-clamped position. This may occur, for example, when the clamping assembly is used in a hydraulic winch which is required to be capable not only of exerting traction on a cable for raising a load, but also of paying out the cable progressively in order to lower the load. To this end, proposals have already been made to associate at least one auxiliary hydraclic actuator with the two jaws of the clamping assembly, such that when the actuator is actuated it pushes the two jaws towards their second position (see U.S. Pat. No. 4 615 509, for example). When the second above-mentioned spring is provided, it is then sufficient to use a single-acting hydraulic actuator for said auxiliary jaw-controlling actuator. However, when second springs are not provided, it is necessary to use a double-acting actuator for the auxiliary hydraulic actuator, and this requires a hydraulic fluid distributor to be used which is more complicated than would be required for a single-acting actuator.
The object of the present invention is therefore to provide a clamping assembly in which it is possible to use a single spring for each jaw while nevertheless providing the functions which used to be provided by the above-mentioned first and second springs, so that if the jaws are to be controlled positively, it is still possible to use an auxiliary actuator which is a single-acting actuator in spite of using only one spring.